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Required depth of footer inside an existing foundation

I have a very old home (circa 1840) and on the back of the home a wood shed was attached over the years on top of a stone foundation. The house is very solid all the way around and this 14 X 18 foot wood shed is my future kitchen.

The existing floor is too soft/spongy and will require a tear out with new joists and subfloor. The walls and ceilings have already been re-framed with 6 inch timber and new insulation added.

I have not opened the floor up yet and am only speculating on the job at hand. (I am not in NY where the house is) I am wondering if I could dig a "footer" in the crawl space around the inside of the existing foundation? What depth would it need to be dug to? If i can do this and lay a level layer of cement block it will give me a solid square and level platform to build on.

Thanks in advance.


Re: Required depth of footer inside an existing foundation

Its always important to check with your local building department for codes on footer depth. I dont know about NY but down south the average depth on any home footer is going to be roughly twelve inches.

Re: Required depth of footer inside an existing foundation

Your best bet is to check the local building codes before you do anything. I'm originally from Pennsylvania near Pittsburgh (go steelers)and the code for a footer was three feet deep because of the winter temperatures. In the mountains the requirement was even deeper. I'm not sure about digging "inside" the perimeter of the building for the footer. You want your footer to be "DIRECTLY UNDER" the wall you are supporting. From what you've said I would say you need to "pin" up one side of the wall dig and pour your footer and they lay concrete block to come up to sill plate level. You could also build forms to make your footer be a concrete wall instead of using block. Good Luck. Check Codes!

Calcats ;)

Re: Required depth of footer inside an existing foundation

Except for the fact that you have a wood shed with a stone foundation, you didn't mention that the old foundation is failing. Chances are the proper depth is at least 3 feet. The local building department or any local contractor can tell you the proper depth.
If the old foundation isn't the proper depth deep, then under pinning the old wall is the thing to do. One problem though is trying to underpin a wall that probably doesn't have a footing to hold it up as you work.
Another option would be to replace the existing stone foundation with a new spread footing and foundation.
A good contractor(s) should be able to give you some ideas. Underpinning or replacing the foundation isn't really a DIY job unless you are experienced or have access to experienced help.

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